Kate Middleton attends a school parent's event

The Duchess of Cambridge has attended a school parents' event using a secret entrance attached to a pub in London.

Kate Middleton met with other parents from Thomas's school in Battersea, attended by her eldest children Prince George, six, and Princess Charlotte, four.

Prince George has attended the school since 2017 and Princess Charlotte began at the school in September 2019.

The Duchess has joined other school parents for a gathering at a local pub. (AP)

When Princess Charlotte's enrolment at the school was announced, Simon O'Malley, headmaster at Thomas's said: "We are delighted that the Duke and Duchess of Cambridge have decided that Princess Charlotte will join her elder brother, Prince George, at Thomas's Battersea.

"We greatly look forward to welcoming her and all of our new pupils to the school in September".

The parent's gathering for Thomas's parents was held at the Hollywood Arms hotel in Chelsea, and it is thought the secret entrance to the pub is left over from when Prince Harry used to visit the venue during his younger years.

The venue is popular for its weekend brunches and Sunday lunches.

Princess Charlotte, four, began school in 2019. (AP)

Kate, 37, has had a busy few weeks, having recently returned from a royal tour to Pakistan with Prince William.

Over the school holidays, she was spotted browsing for Halloween outfits in a Sainsbury's supermarket in Norfolk ahead of the October 31 event.

Her two eldest children - Prince George and Princess Charlotte - attend the school. (AP)

The Duke and Duchess of Cambridge are said to be keen for their children, including Prince Louis, one, to live as normal an existence as possible.

"Kate has always wanted the children to live in the real world," a source told The Sun. "She and William don't want them to live in a gilded bubble. They want them to grow up having the same experiences as other kids."